Instance names are occasionally reported in driver error messages. You can determine the binding of an instance name to a physical name by looking at dmesg(1M) output, as in the following example.
sd9 at esp2: target 1 lun 1 sd9 is /sbus@1,f8000000/esp@0,800000/sd@1,0 <SUN0424 cyl 1151 alt 2 hd 9 sec 80>
Once the instance name has been assigned to a device, it remains bound to that device.
Instance numbers are encoded in a device's minor number. To keep instance numbers consistent across reboots, the system records them in the /etc/path_to_inst file. This file is read only at boot time, and is currently updated by the add_drv(1M) and drvconfig(1M) commands. See the path_to_inst(4) man page for more information.